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BobLfoot

Panel Thermal Management

6 posts in this topic

Several panels we've recently because of Servo, VFD and other Heat Producing Component inside have come with Side Mount AC Units similiar to those found here -- http://www.hoffmanonline.com/product_catalog/product_detail.aspx?cat_1=34&cat_2=2383&cat_3=79449&catID=79449&itemID=3532 I am wondering since we have a chilled water loop {glycol actually} for cooling in several other parts of our process if switching to a Water to Air Heat Exchanger similiar to these http://www.rittal.ca/products/index.cfm?n1ID=4&n2ID=14&n3ID=24 would be more cost effective in the long run. Rather than a compressor unit drawing 13.5 FLA I'd ahve the fan unit drawing 0.5 FLA. Obviously the glycol system would see increased thermal load but this is nominal given the efficiencies of the NH3 Plate-Frame chiller which cools the glycol. Anyone with experience with both type of Thermal management have any input? Horror stories or gotchas welcome.

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The plant I work in uses a chilled water supply to control the temperatures of extruders, mixers and injection molding machines. We do not, however, use the chilled water system to control the temperatures in our electrical cabinets. It is a novel idea, but here are some things to consider: 1) What is the temperature of the chilled water supply at the point where the heat exchanger will be installed? This is important to think about because if your water supply is less than dewpoint of the ambient air, then condensation could be an issue. This can be an issue with AC units as well, but some of the better ones have appropriate dissipation methods to burn off the condensate. AC units also have temp controllers to limit how low the temp can get. 2) I did not see if there were any controls in the heat exchangers. Specifically, will water flow to the exchanger be stopped when there is no need for cooling? If not, will you add it? This could be helpful in controlling #1 above and could help reduce the heat load on your chilled water system. I am interested in the results if you decide to use the heat exchangers coupled to your chilled water system. Keep us posted on your decision and results.

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I worked at a plant that had huge induction heating units. (You know where) Each unit had it's own cooling tower I did several panel cooling jobs by tapping into the existing cooling circuits. I did cycle the water thru the coil to reduce the effects on possible moisture from condensation. I use a type-j to see temp and only allowed the panel temp to drop 5° at a time. Then I would wait until the temp raised 2 ° then allow another 5° drop. This way you don't reduce the temperature to rapidly and cause condensation.

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That's genius, Jeff. We have panels melting down in a room that is kept at 45 degrees F. I am going to investigate flange mounting a VFD I think.

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Not genius, just a little HVAC background. Another one of those license I pay $200/year to keep in my wallet. If you have the a PLC in that panel you can look at a dew point meter and run the cooling coil to within a few degrees of the dew point. If you do that pay attention to a surface condensation. IN a normal HVAC system you can get 100% relative humidity just after the coil in the duct. This is because of how dense the air is directly after the coil. Take that same reading 24" out side of the duct and your dew point is way down. It is usually recommended to take your measurement at the intake of the coil. Just a little useless info for you.

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One thing to keep in mind. No heat exchanger, water-cooled or otherwise, is going to perform as well as an air conditioner. The reason is because an A/C system manipulates boiling points. It takes 1 btu to heat one pound of water 1 degree. So if you had a pound of water (about a pint), it would take 1 btu to heat it from 211 to 212 degrees. But to actually boil that water and turn it into steam would take 970 btu. When the refrigerant in the evaporator of an A/C boils, it is removing hundreds of times the heat from the panel a simple heat exchanger would.

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